prod(numeric(0)) surprise
I'm a little confused. I understand that numeric(0) means an empty numeric vector, not the number 0 expressed as numeric. As it is now, prod(numeric(0)) generates something -- a vector of length 1 containing the number 1 -- from nothing. I would have expected prod(numeric(0)) ==> numeric(0) this is consistent with numeric(0) ==> numeric(0) numeric(0) * 1 ==> numeric(0) cumprod(numeric(0)) ==> numeric(0) and, because concatenation occus before function evaluation, prod(c(numeric(0),1)) ==> prod( c(1) ) ==> 1 I would expect sum() to behave the same way, e.g., sum(numeric(0)) ==> numeric(0). From below,
>>>> consider exp(sum(log(numeric(0)))) ... ?)
>>
>> That's a fairly standard mathematical convention, which
>> is presumably why sum and prod work that way.
>>
>> Duncan Murdoch
I would have expected numeric(0) as the result (numeric(0) is the result from log(numeric(0)), etc). Martin (Morgan) Martin Maechler <maechler at stat.math.ethz.ch> writes:
"Ben" == Ben Bolker <bolker at zoo.ufl.edu>
on Sun, 08 Jan 2006 21:40:05 -0500 writes:
Ben> Duncan Murdoch wrote:
>> On 1/8/2006 9:24 PM, Ben Bolker wrote:
>>
>>> It surprised me that prod(numeric(0)) is 1. I guess if
>>> you say (operation(nothing) == identity element) this
>>> makes sense, but ??
>>
>>
>> What value were you expecting, or were you expecting an
>> error? I can't think how any other value could be
>> justified, and throwing an error would make a lot of
>> formulas more complicated.
>>
>>>
>>
>>>> consider exp(sum(log(numeric(0)))) ... ?)
>>
>> That's a fairly standard mathematical convention, which
>> is presumably why sum and prod work that way.
>>
>> Duncan Murdoch
Ben> OK. I guess I was expecting NaN/NA (as opposed to
Ben> an error), but I take the "this makes everything else
Ben> more complicated" point. Should this be documented or
Ben> is it just too obvious ... ? (Funny -- I'm willing to
Ben> take gamma(1)==1 without any argument or suggestion
Ben> that it should be documented ...)
see? so it looks to me as if you have finally convinced
yourself that '1' is the most reasonable result.. ;-)
Anyway, I've added a sentence to help(prod) {which matches
the sentence in help(sum), BTW}.
Martin
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